Geothermal heat pump system having a downflow appliance cabinet

ABSTRACT

A compact, down-flow appliance cabinet for indirect-exchange heat pump systems has a bottom panel that incorporates a mounting plate for the compressor and a lower rectangular aperture for the exit of conditioned air. A center shelf parallel to the bottom platform divides the cabinet into upper and lower chambers and provides a mounting location for a blower assembly within the upper chamber on top of a middle aperture. An air duct interconnects the middle and lower rectangular apertures. A top cover incorporates an air filter mount and an upper rectangular aperture that couples to the return air duct. Diagonally-positioned radiator mounts, which are secured to the cabinet frame, provide a mounting location for the evaporator coil. A desuperheater heat exchanger mounts within the lower chamber adjacent the heat pump; a refrigerant/ground loop heat exchanger mounts within the upper chamber beneath the radiator mounts.

This application has a priority date based on the filing of Provisional Patent Application No. 61/224,425, of the same title, on Jul. 9, 2009. BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, generally, to geothermal heat pump systems and, more particularly, to a downflow appliance cabinet in which heat exchanger units and the compressor are located.

2. History of the Prior Art

A heat pump is a machine or device that moves heat from one location (the heat source) to another location (the heat sink) using mechanical work. The heat pump was imagined by Lord Kelvin in 1852 and developed by Peter Ritter von Rittinger in 1855. Most heat pumps are employed to move heat from a low temperature heat source to a higher temperature heat sink. Common examples are food refrigerators and freezers, air conditioners, and reversible-cycle heat pumps which provide both cooling and heating functions. In heating, ventilation, and air conditioning (HVAC) applications, the term heat pump normally refers to a vapor-compression refrigeration device that includes a reversing valve and optimized heat exchangers so that the direction of heat flow may be reversed. Standard reversible heat pumps draw heat from the air for heating applications and sink heat to the air for cooling applications. Although they are particularly efficient and cost-effective when outside air temperature are not dramatically different from a desired interior temperature, air-source heat pumps used for heating do not work as well when air temperatures fall below around −5° C. (23° F.).

A geothermal heat pump (also known as a ground source heat pump, water-source heat pump, and earth-coupled heat pump) is a highly efficient renewable energy technology that is gaining wide acceptance for both residential and commercial buildings because it avoids the limitations of air source heat pumps. Geothermal heat pumps are used for space heating and cooling, as well as water heating. Its great advantage is that, rather than producing heat through the combustion of fossil fuels, it works by using the earth as a heat source for heating a building and as a heat sink for cooling the building. After experimenting with a freezer, Robert C. Webber built the first direct-exchange ground-source heat pump in the late 1940s. The first successful commercial project was installed in the Commonwealth Building of Portland, Oreg. in 1946. The technology became popular in Sweden in the 1970s, and has been growing slowly in worldwide acceptance since then. Open loop systems dominated the market until the development of polybutylene pipe in 1979 made closed loop systems economically viable. As of 2004, there are over a million units installed worldwide providing 12 GW of thermal capacity. Each year, about 80,000 new units are installed in the USA and 27,000 in Sweden.

Geothermal heat pump technology relies on the fact that several feet below its surface (i.e., below the frost line), the earth's crust remains at a relatively constant temperature throughout the year. Thus, it is warmer than the ambient air during the winter, and cooler in the summer. A geothermal heat pump takes advantage of this phenomena by transferring heat stored either in the earth's crust or in ground water into a building during the winter, and transferring heat out of the building and back into the earth's crust or ground water during the summer. In other words, the ground acts as a heat source in winter and as a heat sink in summer.

A geothermal heat pump system includes three principal components: a geothermal earth connection subsystem; a heat pump subsystem; and a heat distribution subsystem. A geothermal heat pump system may also include a fourth component called a desuperheater coil. The desuperheater coil recovers the waste heat discharged from the compression cycle of the heat pump and transfers that heat to water in the water heater. Thus, heat that would otherwise be wasted is recovered and used to heat water. Heat recovery works by extracting heat from the refrigerant as it leaves the heat pump compressor and transferring that heat into the water within the water heater. The more efficient, high SEER heat pumps run with lower refrigerant temperatures so they don't heat water as fast as the lower SEER models. However, as long as the refrigerant temperatures are over 130° F., the heat can be effectively transferred to water in the water heater. Heat recovery for the heating of water actually increases the efficiency of the heat pump system by about ten percent. It also reduces the head pressure on the compressor; thereby reducing stress and extending the service life of the compressor. Thus heat recovery offers three benefits: free hot water, reduced heating and air conditioning costs, and decreased wear and tear on the heat pump.

Direct-exchange geothermal heat pump systems are the oldest and conceptually easiest geothermal systems to understand. The ground-coupling is achieved through a single loop of refrigerant in direct thermal contact with the ground. The refrigerant leaves the heat pump appliance cabinet, circulates through a loop of copper tube buried underground, and exchanges heat with the ground before returning to the pump. The name “direct exchange” refers to heat transfer between the refrigerant and the ground without the use of an intermediate fluid. There is no direct interaction between the fluid and the earth; only heat transfer through the walls of the pipe. Direct-exchange heat pumps are usually excluded by the terms “water-source heat pumps” or “water loop heat pumps,” as there is no water in the ground loop. Direct-exchange systems are 20-25% more efficient and have potentially lower installation costs than closed loop water systems. While they require much more refrigerant and their tubing is more expensive per foot, a direct-exchange loop may be much shorter than a closed water loop. As a direct-exchange system requires one-third to one-half the length of tubing, and the diameter of holes drilled for vertical closed loops can be halved, drilling or excavation costs are therefore lower. Tubing must be made of copper to contain the refrigerant pressure and to allow high quality joints that will not leak the refrigerant. In addition, the copper loop must be protected from corrosion in acidic soil through the use of a sacrificial anode. Although marketing materials often emphasize the high thermal conductivity of copper, heat flow is primarily limited by the thermal conductivity of the ground, rather than that of the material from which the pipe for the refrigerant loop is made.

Indirect-exchange heat pump systems are double loop systems requiring a heat exchanger between a refrigerant loop and a secondary loop and pumps in both loops. Some manufacturers have a separate ground loop fluid pump pack, while some integrate the pumping and valving within the heat pump. Expansion tanks and pressure relief valves may be installed on the heated fluid side. The lower efficiency of closed loop systems requires longer and larger pipe to be placed in the ground, increasing excavation costs. Most installed systems have two loops: a primary loop containing refrigerant is contained in an appliance cabinet, where it passes through an internal heat exchanger that is coupled to a secondary loop containing a mixture of water and antifreeze (propylene glycol, denatured alcohol or methanol). The secondary loop, which is typically made of high-density polyethylene tubing, is either buried in a trench below the frost line, or buried in a vertically-oriented hole drilled in the ground. After leaving the internal heat exchanger, the water/antifreeze mixture flows outside the temperature-controlled building through the secondary loop where heat is exchanged between the ground and the mixture before it returns to the internal heat exchanger. outside the building to exchange heat with the ground before returning. If a nearby body of water is available, the secondary loop may be submerged therein. Secondary loops in wet ground or in water may be much shorter than those in dry ground because of the superior thermal conductivity of water. If the ground is naturally dry, soaker hoses may be buried with the ground loop to keep it wet.

Closed secondary loop tubing can be installed horizontally as a loop field laid in trenches or vertically as a series of long U-shapes in wells (see below). The size of the loop field depends on the soil type and moisture content, the average ground temperature and the heat loss and or gain characteristics of the building being conditioned. A rough approximation of the initial soil temperature is the average daily temperature for the region.

A horizontal closed loop field is composed of pipes that run horizontally in the ground. A long horizontal trench, deeper than the frost line, is dug and U-shaped or slinky coils are placed horizontally inside the same trench. Excavation for horizontal loop fields is about half the cost of vertical drilling, so this is the most common layout used wherever there is adequate land available. For illustration, a detached house needing 10 kW (3 ton) of heating capacity might need 3 loops 120 to 180 m (400 to 600 feet) long of ¾ inch (19 mm) or 1.25 inch inside diameter polyethylene tubing at a depth of 1 to 2 m (3 to 6 feet). A slinky, or coiled, closed loop field is a type of horizontal closed loop where the pipes overlay each other. A slinky loop field is used if there is not adequate room for a true horizontal system, but it still allows for an easy installation. Rather than using straight pipe, slinky coils use overlapped loops of piping laid out horizontally along the bottom of a wide trench. Depending on soil, climate and your heat pumps' run fraction, slinky coil trenches can be anywhere from one third to two thirds shorter than traditional horizontal loop trenches. Slinky coil ground loops are essentially a more economic and space efficient version of a horizontal ground loop.

A vertical closed loop field is composed of pipes that run vertically in the ground. A hole is bored in the ground, typically, 75 to 500 plus feet deep. Pipe pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole. The borehole is commonly filled with a bentonite grout surrounding the pipe to provide a good thermal connection to the surrounding soil or rock to maximize the heat transfer. Grout also protects the ground water from contamination, and prevents artesian wells from flooding the property. Vertical loop fields are typically used when there is a limited area of land available. Bore holes are spaced 5-6 m apart and the depth depends on ground and building characteristics. For illustration, a detached house needing 10 kW (3 ton) of heating capacity might need 3 boreholes 80 to 110 m (270 to 350 feet) deep. [5] (A ton of heat is 12,000 British thermal units per hour (BTU/h) or 3.5 kilowatts.) During the cooling season, the local temperature rise in the bore field is influenced most by the moisture travel in the soil.

A closed pond loop is not common because it depends on proximity to a body of water, where an open loop system is usually preferable. However, a closed pond loop may be advantageous where poor water quality precludes an open loop, or where the system heat load is small. A pond loop consists of coils of pipe (similar to a slinky loop) attached to a frame and located at the bottom of an appropriately sized pond or water source.

Open loop systems using ground water in the secondary loop are usually more efficient than closed systems because they are better coupled to ground temperatures. Closed loop systems, in comparison, have to transfer heat across extra layers of pipe wall and dirt. In an open loop system, (also called a groundwater heat pump,) the secondary loop pumps natural water from a well or body of water into a heat exchanger inside the heat pump. ASHRAE calls open loop systems groundwater heat pumps or surface water heat pumps, depending on the source. Heat is either extracted or added by the primary refrigerant loop, and the water is returned to a separate injection well, irrigation trench, or body of water. The supply and return lines must be placed far enough apart to ensure thermal recharge of the source. Since the water chemistry is not controlled, the appliance must be protected from corrosion by using different metals in the heat exchanger and pump. Limescale may foul the system over time and require periodic acid cleaning. Also, as fouling decreases the flow of natural water, it becomes difficult for the heat pump to exchange building heat with the groundwater. If the water contains high levels of salt, minerals or hydrogen sulfide, a closed loop system is usually preferable. Deep lake water cooling uses a similar process with an open loop for air conditioning and cooling.

A standing column well system is a specialized type of open loop system. Water is drawn from the bottom of a deep rock well, passed through a heat pump, and returned to the top of the well, where traveling downwards it exchanges heat with the surrounding bedrock. The choice of a standing column well system is often dictated where there is near-surface bedrock and limited surface area is available. A standing column is typically not suitable in locations where the geology is mostly clay, silt, or sand. If bedrock is deeper than 200 feet (61 m) from the surface, the cost of casing to seal off the overburden may become prohibitive.

The appliance cabinet of an indirect-exchange (double loop) heat pump system typically contains at least the following system components: the heat pump, the refrigerant loop, the heat exchanger between the refrigerant loop and the secondary ground or water loop, the heat exchanger between the refrigerant loop and the internal air, an electrically-powered blower to more air through the refrigerant/air heat exchanger, and all necessary system control circuitry. Only the secondary ground or water loop and the air ducts which direct air from the refrigerant/air heat exchanger are missing from the appliance cabinet. A fourth component that is frequently contained within the appliance cabinet is a desuperheater heat exchanger coil that is immediately adjacent the heat pump. Appliance cabinets for indirect-exchange geothermal heat pump systems have heretofore been horizontal flow units requiring a large foot print. The large footprint required by such appliance cabinets necessarily requires a large utility room. As most builders minimize the costs of new construction by installing inexpensive, low-efficiency down-flow furnaces in utility rooms or closets of the minimum required size, the retrofit installation of indirect-exchange heat pump systems in existing structures has been severely limited by the lack of utility closets and utility rooms of sufficient size to house the available horizontal-flow units.

What is needed is a compact down-flow utility cabinet for indirect-exchange (double loop) heat pump systems.

SUMMARY OF THE INVENTION

The present invention provides a compact down-flow appliance cabinet for indirect-exchange heat pump systems. The cabinet includes left and right front corner posts and a rectangular rear panel that incorporates spaced apart left and right rear corner posts. An front door and lower front panel are secured to the front corner posts. A bottom cover, which is secured to the lower ends of all four corner posts, incorporates a mounting plate, or base, for the compressor and a lower rectangular aperture for the exit of air traveling through the appliance cabinet. A center shelf parallel to the bottom cover divides the cabinet into upper and lower chambers and provides a mounting location for a fan assembly within the upper chamber on top of a middle aperture. An air duct interconnects the middle and lower rectangular apertures. A top cover incorporates an air filter holder, as well as an upper rectangular aperture that couples to the return air duct. Front and rear diagonally-positioned mounting radiator mounts are secured to the cabinet frame within the upper chamber. The evaporator coil of the system is affixed to the radiator mounts. A desuperheater heat exchanger is affixed to a lower coil mount that is affixed to the rear panel within the lower chamber adjacent the heat pump. A refrigerant/ground loop heat exchanger is affixed to an upper coil mount that is affixed to the rear panel within the upper chamber beneath the radiator mounts for the evaporator coil. Thus, the refrigerant loop passes through the compressor, through the desuperheater coil, through the refrigerant coil of the refrigerant/ground loop heat exchanger, through the evaporator coil, and back to the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is an isometric view of the downflow appliance cabinet for a geothermal heat pump system, with the front, and side panels removed;

FIG. 2 is an isometric view of the downflow appliance cabinet of FIG. 1 with the front and side panels in place;

FIG. 3 is a left side elevational view of the downflow appliance cabinet of FIG. 1;

FIG. 4 is a front elevational view of the downflow appliance cabinet of FIG. 1;

FIG. 5 is a right side elevational view of the downflow appliance cabinet of FIG. 1;

FIG. 6 is a front elevational view of the downflow appliance cabinet of FIG. 1, with the front panel removed;

FIG. 7 is a top plan view of the downflow appliance cabinet of FIG. 1; and

FIG. 8 is a thin section view of the downflow appliance cabinet of FIG. 1, with the front and side panels removed, through section plane A-A, showing only the rear panel and the right and left corner posts in profile.

DETAILED DISCLOSURE OF THE INVENTION

The present invention will now be described in detail with reference to the attached drawing figures.

Referring now to FIG. 1, the downflow appliance cabinet frame 100 for geothermal heat pump systems includes a right front corner post 1, a left front corner post 102, a rear panel 103 which incorporates left and right rear corner posts, a top cover 104, a bottom cover 105, and a center shelf 106. A left side lower panel 8 and a left side upper door 10, which are visible in this drawing figure, have been secured to the cabinet frame 100. A diagonally-oriented front radiator (evaporator) mount 111 is secured at the top thereof to the front left corner post 102, and at the bottom thereof to the right corner post 101. A diagonally-oriented rear radiator mount 112 is secured to the between the rear left and right corner posts of the rear panel 103. The system's evaporator coil is secured to the front and rear radiator mounts 111 and 112, respectively. A drip pan 113 is secured between the lowermost ends of the front and rear radiator mounts 111 and 112. An upper coil mount 114 positioned beneath the rear radiator mount 112 and affixed to the rear panel 103 provides a mounting location for the system's refrigerant/ground loop heat exchanger. The refrigerant/ground loop heat exchanger is secured with an upper coil hold down bracket 115. The center apertures of the upper coil hold down bracket 115 and of the upper coil mount 114 are coaxial, with the upper coil hold down bracket 115 shown spaced away from the upper coil mount 114. A bolt and nut (not shown) will be used to secure the upper coil hold down bracket 115 and the upper coil to the upper coil mount 114. An lower coil mount 116 positioned beneath the center shelf 106 and secured to the rear panel 103 provides a mounting location for the system's desuperheater heat exchanger, which transfers heat generated by operation of the heat pump to the hot water tank. The desuperheater heat exchanger is secured with a lower coil hold down bracket 117. The center apertures of the upper coil hold down bracket 117 and of the lower coil mount 116 are coaxial (neither aperture is visible in this view), with the upper coil hold down bracket 117 shown spaced away from the upper lower mount 116. A bolt and nut (not shown) will be used to secure the lower coil hold down bracket 117 and the lower coil (not shown) to the lower coil mount 116.

Still referring to FIG. 1, the center shelf 106 incorporates a fan mounting angle 120, which surrounds a middle rectangular aperture within the center shelf 106. The bottom cover 105 incorporates a compressor base 119 and a lower rectangular aperture for the exit of air traveling through the cabinet. An air duct 118 interconnects the middle and lower rectangular apertures. A top cover 104 incorporates a filter holder 121, which surrounds an upper rectangular aperture that couples to the return air duct.

Referring now to FIG. 2, a front upper door 202, a front lower panel 201, a right side upper door 110 and a right side lower panel 108 have been installed on the appliance cabinet frame 100, thereby completing the appliance cabinet 200. It will be noted that the right-side and left-side upper doors 110 and right-side and left-side lower panels 108 are identical.

FIGS. 3, 4, 5 and 7 provide additional views of the complete appliance cabinet 200, while FIGS. 6 and 8 provide additional views of the appliance cabinet frame 100.

Although only several embodiments of the present invention have been disclosed herein, it will be obvious to those having ordinary skill in the art that changes and modifications may be made thereto without departing from the scope and spirit of the invention as hereinafter claimed. 

1. A down-flow appliance cabinet for indirect-exchange heat pump systems comprises: a generally rectangular cabinet structure having a rear panel; right and left front corner posts; a top cover having an air intake opening; a bottom cover having a conditioned air exit; a central shelf having a central aperture incorporating a fan mount; an air duct coupling the conditioned air exit and the central aperture; a radiator frame diagonally positioned above the central shelf; an upper coil mount secured to the rear panel above the central shelf; a lower coil mount secured to the rear panel below the central shelf; a compressor base secured to the bottom cover; and a plurality of covers to fully enclose the front and sides of the cabinet structure.
 2. The down-flow appliance cabinet of claim 1, wherein said upper coil mount is intended to hold a refrigerant/ground loop heat exchanger mounted within the upper chamber beneath the radiator frame and said lower coil mount is intended to hold a desuperheater heat exchanger. 